With continuous evolution of wireless cellular networks, although widely applied to third-generation (“3G” for short) and fourth-generation (“4G” for short) mobile communications systems, orthogonal multiple access technologies such as a code division multiple access (“CDMA” for short) technology and an orthogonal frequency division multiple access (“OFDMA” for short) technology have gradually failed to meet people's increasing capacity requirements in cellular networks. For example, massive accesses and spectral efficiency need to continue increasing. On the other hand, research and application of non-orthogonal multiple access technologies gradually draw more attention in the industry and academic communities. People hope that in a future wireless cellular network such as a fifth-generation (“5G” for short) mobile communications system, a capacity improvement problem can be effectively resolved with the aid of the non-orthogonal multiple access technologies.
A sparse code multiple access (“SCMA” for short) technology is a typical non-orthogonal multiple access and transmission technology. Certainly, the SCMA technology may be referred to as another name in the communications field. In this type of technology, M (M is an integer not less than 1) data streams from one or more users are superimposed on N (N is an integer not less than 1) subcarriers and sent. Each piece of data in each data stream is spread on the N subcarriers in a sparse spread-spectrum form. When M is greater than N, this type of technology can effectively increase network capacity, including a quantity of users who can access a system, spectral efficiency, and the like. Therefore, as an important non-orthogonal access technology, the SCMA technology has drawn a lot of attention, and becomes an important candidate access technology for evolution of future wireless cellular networks.
In a non-orthogonal multiple access system such as an SCMA system, when sending an uplink data stream by using a non-orthogonal multiple access technology, a terminal device needs to know a codebook used for the uplink data stream. A network device usually completes selection and assignment of a codebook, and the terminal device does not directly participate in this process. Therefore, after the network device assigns a codebook to a data stream that is to be sent to the terminal device, how to inform the terminal device of the assigned codebook is a technical problem that urgently needs to be resolved.